Mechanical Fuel Pump Repair Questions

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michaelbalk330
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Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sun Jan 31, 2016 12:15 am

I decided to get my 330 GT mechanical working again so I rebuilt it, and found the diaphragm and valves all OK. While it clearly hadn't been rebuilt in decades, and someone had replaced the Pin that runs thru the body with a bolt and nut ( its the pin the hammer pivots on), the real issue wasn't the rubber pieces. The Hammer head was slightly worn ( pic ) and the bolt was slightly smaller diameter so there was excess movement of the hammer and assembly and not that much force is exerted on the Diaphragm when the hammer is hit. Its really a crappy design that any high school physics student could elucidate, and the "lever" action is poor, and the design lets this slight wear really become an issue.

Now that its all back together, everything is tight mechanically as designed, with new pins, valves and gaskets. It works- but I still get low fuel pressure. I can drive the car and it doesnt stall ( which is used to do at idle within a very short amount of time after turning off the Electronic pump) . But if I drive at 3-4000 RPM for a minute, the pump can't keep up. The regulator never fills more than 25% ( where as with the e-pump its full).

My question is this:
I have already made the phenolic spacer block a bit thinner.
Do I continue to make it thinner until I get adequate PSI?

I have clearly made progress, but I would like to have my mechanical pump work perfeclty. I am sure the pump it put together correctly as I can hear and feel the diaphragm movement and pumping action, and have rebuilt numerous other fuel pumps.

Michael
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Michael
1967 330GT #9693
1967 Ducati 350 Sebring #04783

Jumprun
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Re: Mechanical Fuel Pump Repair Questions

Postby Jumprun » Sun Jan 31, 2016 1:24 am

Welcome to one of the most troublesome features of our cars. There are volumes written on this site about these darned pumps. One tip besides searching the site is to make sure the pins, plates and rods have as little slop as possible in order to reduce the amount of free play before the diaphragm is moved because there is so little stroke produced by the push pin you can not afford to waste any of it. Thinning out the spacer is the common approach but only take a small amount at a time because too thin is not good either. Even the thickness of the gasket makes a difference. Check the push pin stroke, I forgot what it's supposed to be, I think it's 3-4 mm but do a search to see what others say.
Check the flatness of the mounting face, mine was really warped from over tightening requiring some precision belt sander work, this flattening had the same effect as thinning the spacer.

I removed my pump nearly a dozen times before I got it to work within it's narrow tolerance band.

Good luck, Tom in SoCal

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John Vardanian
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Re: Mechanical Fuel Pump Repair Questions

Postby John Vardanian » Sun Jan 31, 2016 1:30 am

Michael, given the mods you described, it's possible that the tabs may be incorrectly installed upside down, and if they are, by putting them right you would gain in stroke. There is an old discussion on this forum that discusses this and shows a diagram.

john
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michaelbalk330
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Re: Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sun Jan 31, 2016 7:40 am

John and Tom
thanks for responding.

i read all the posts before doing the rebuild- I think tabs are installed correctly.
But there is one confusing part from those posts- on my car, there is only ONE way the tabs can be installed.
Bolt A ( or pin A as OEM) only fits in Hole A, and pin B only fits in Hole B ( which is where the diaphragm stud connects to the assembly).

The only thing theoretically that one might mess up is installing those metal tabs backwards, but they are bevel cut ( sort of chamfered) and if you accidentally try to install them backwards, they wont fit.
So that part of the prior posts never made any sense to me.

Lastly, I am using no gasket on the phenolic block, as that was also mentioned in prior posts. I even shot a video of the actuator moving as I turn the engine so I know that cam driven pushrod is working. All the linkages are good and no slop. it works at low RPM ... I just need more movement of the hammer to increase supply as RPM rises.

From my college physics, all that would be needed is a new hole further up the tabs, move the pin into that new hole, and make the hammer taller ( 3d printer) so it strikes the pin further up---- increasing the lever action.
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Michael
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cory
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Re: Mechanical Fuel Pump Repair Questions

Postby cory » Sun Jan 31, 2016 8:36 am

I have just gone through the same issues with my pump and as was said earlier, there are volumes written here about all these issues. I will explain what I found. My mechanical pump was only putting out a little over 1 psi, at the pump and regulator. Make sure you have checked the psi pre regulator to eliminate it as the possible culprit. My pump was rebuilt using a rebuild kit from the usual suspects. All appeared ok, hit pin not worn, rocker arm not worn, all pieces orientated in the right positions but still not the correct psi. I sent the pump to "Then and Now" in Weymouth Mass. They felt that the top cap sealing material was to "thick" and not helping the low psi issue. It was changed (extremely cheap I may add). In the mean time they also found a little debris in the pump. I had the tank flushed, pressure tested and re done about 2 years ago. As there was only apx 1000 miles on the car I drained and flushed the tank anyway. In checking the pick up tube I found the slightest 1/2" long crack that was barely noticeable. I re soldered a new pick up tube in place. I changed the rear most fuel filter and also checked and cleaned the steel fuel line leading to the mechanical fuel pump. Checked measurements and did the math to get the most stroke without the chance of the rocker arm breaking and took a little off of the pump spacer and reinstalled, without gaskets. The pump now registers over 3 psi.
Bottom line: Being that todays fuels are not really friendly in working with such low psi's that our cars use every little advantage is needed. Without taking the time to check over every detail leading to the mechanical fuel pump I could have been chasing this down for a while as I believe it was a combination of problems leading to my low psi.
Double check your measurements to get the most throw out of the pump.
Make sure your fuel level is under 1/4 tank and remove/check pickup tube.
I haven't read your entire post so sorry if I am repeating what has already been posted but feel free to contact me if I can help being that this was a fresh repair for me.
Cory

DWR46
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Re: Mechanical Fuel Pump Repair Questions

Postby DWR46 » Sun Jan 31, 2016 11:44 am

The pushrod stroke is about .096". A .025" change in stroke is a 25% change!! Mount the pump with the lower cover off the pump, and them turn the motor over by hand to measure if you are getting full stroke. Find the point of full stroke and see if you can still move the diaphragm. if so, remove a small amount of the spacer or a gasket if one is present. Do this until you have only a small amount of "excess" diaphragm movement available to insure you are not overstroking the pump. Then you will have the maximum possible pumping action.

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michaelbalk330
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Re: Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sun Jan 31, 2016 4:56 pm

Dyke,
Your plan was what I had planned next. made the most sense to me as I was trying to figure it out.
I can tell I am making progress, and after reading of people pulling the pump 12 times before getting it right, this is what made the most sense to me. Since I have been in there twice, I know exactly how much movement I need to generate the pumping function.
It looks like you can't mount the cover once pump is installed but its now a 5 minute task so no big deal.

LOL --to do the repair I let the gas tank go near empty, and when I drove my car to get gas after finishing the repair,, i drove only in the neighborhood and engine was cold so I kept it under 3K RPM and thought I had it fixed.
SO I FILLED HER UP.
It was only after I had her warmed up and filled the tank that I realized the pump wasn't putting out enough.
So now i HAVE to go drive her and use up the gas. life is tough.
appreciate everyones help.
Cory, how does the suction pipe crack affect the PSI output on the pump?
Michael
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1967 Ducati 350 Sebring #04783

cory
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Re: Mechanical Fuel Pump Repair Questions

Postby cory » Sun Jan 31, 2016 7:51 pm

As you use fuel your head pressure begins to decrease. Eventually you have a possibility of sucking air thru the pick up tube, as the fuel level decreases, in turn affecting fuel psi. I would post pics of the split tube but I don't have a 12 yr old available to show me how to retrieve it and add it to this.
Cory

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michaelbalk330
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Re: Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sun Jan 31, 2016 8:11 pm

Ok then a full tank should alleviate that variable?
Michael
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cory
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Re: Mechanical Fuel Pump Repair Questions

Postby cory » Sun Jan 31, 2016 8:43 pm

Possibly, as long as you kept a full tank of fuel. Keeping a full tank also helps with vapor lock. Not sure how realistic keeping a full tank all the time is though.

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michaelbalk330
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Re: Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sun Jan 31, 2016 9:12 pm

agree.. just from a diagnostic standpoint.
thanks everyone- I know what to do next. I feel pretty good I can get this thing working.
Its not a huge deal but the moment my electronic pump fails, 60 miles from civilization on a rural mountain run in North Ga, I will be happy I did all this.
michael
Michael
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330GT
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Re: Mechanical Fuel Pump Repair Questions

Postby 330GT » Sun Jan 31, 2016 9:19 pm

cory wrote:As you use fuel your head pressure begins to decrease. Eventually you have a possibility of sucking air thru the pick up tube, as the fuel level decreases, in turn affecting fuel psi. I would post pics of the split tube but I don't have a 12 yr old available to show me how to retrieve it and add it to this.
Cory

Here's the one from my car:
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Regards, Kerry
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michaelbalk330
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Re: Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sun Jan 31, 2016 9:30 pm

kerry, cory
is this tube easy access?
do you need to pull the tank?
m
Michael
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1967 Ducati 350 Sebring #04783

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330GT
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Re: Mechanical Fuel Pump Repair Questions

Postby 330GT » Mon Feb 01, 2016 10:13 am

michaelbalk330 wrote:kerry, cory
is this tube easy access?
do you need to pull the tank?
m

No, See http://www.parrotbyte.com/kbc/ferrari/c ... htm#Pickup for more details.

Just have the fuel level below the fitting where the pickup is screwed in. Also, support the fitting as it takes quite a bit of force to loosen the pickup bolt and you don't want to pop a rivet or split a seam on the tank.
Regards, Kerry
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tyang
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Re: Mechanical Fuel Pump Repair Questions

Postby tyang » Mon Feb 01, 2016 11:25 am

Hi Michael,

Also be careful when you pull the pickup out because there's a screen filter on the end that might fall off when it gets to the fitting.

Tom
'63 330 America #5053


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